As for majority of people in this thread: it was an MMORPG. For me, it was Aion. I played this game in summer of 2013 about 14 to 17 hours a day. Wake up at 9, play till 15. Lunch, play from 16 to 20, have dinner. Play from 20.30 to 4.30 in the morning. Sleep till 9, repeat. That was going on for about three months. I was staring at the computer screen so much, my eye muscles would regularly twitch, I was tired almost all the time, my wrists and fingers would be sore from all the clicking. I played the game from 2012 and up to today in on and off periods. I have no idea how much time I have in the game, but if I played the game for 15 hours every day of the month, that's about 3150 hours. A 30 day month has 5040 hours. So over the course of 3 months I put about 9450 hours into the game. And since I played the game for about 5 years, I probably have like 50k hours in the game.

Now I mostly play Overwatch and while it's not to the point of addiction, I still play it a lot. Sometimes I can go up to 8 to 10 hours a day of nonstop gaming.